What’s the issue with Theresa May’s style?

Etiquette expert Jean Broke-Smith, who’s been teaching the art of the curtsy for decades, said: “She makes it look very awkward and drops so low.

“The knees should be virtually connected but hers are about 10 inches apart. How she didn’t fall over, I don’t know. I was trying it just now and I couldn’t balance.”

“I feel a bit sorry for her,” says author and modern manners columnist Sophia Money-Coutts, who admits she was “fascinated” by the very low curtsy. “But I think someone should have a word.

“If you’re a Tory PM stooping like that in front of the Queen, you’re going to get a backlash. Reining it in a bit and doing a neat bob would be less controversial.”

She adds of Mrs May’s technique: “She really goes in for the curtsy. I’m half her age, but my knees would go snap, crackle and pop if I tried it.”

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But Ms Broke-Smith, who was principal of the Lucie Clayton finishing and modelling school for 30 years, praised the prime minister.

She said: “The most important thing is that she is respectful – and just look at that eye contact with Prince William and that smile.”

So how exactly are you meant to curtsy?

Adam Partridge from etiquette guide Debrett’s, says it should be a “brief, discreet movement” lasting “a matter of seconds”. Here’s his step-by-step guide:

From standing, transfer your weight onto one foot, usually the left

Place the ball of your other foot behind and slightly outside the standing ankle

Bend your front knee, always maintaining eye contact

Image copyrightGetty Images

BBC royal correspondent Jonny Dymond advises that “a straight back is everything”.

He says: “There’s no need to drop towards the floor clutching your skirts in the presence of a Royal Highness. Ladies (and gents) are permitted a bow, or even a (significant) inclination of the head. More than a nod, please.

“If you are going for the curtsy you want a straight back, to mitigate the chances of toppling forwards into a Royal personage. Overdoing eye contact might be seen as showing off.

“Do not curtsy too deep. Obviously struggling to return to a standing position is judged unseemly in royal circles.

“Finally, do not appear too smug as you complete the flawless curtsy.”

So why curtsy instead of shaking hands?

Many people choose to curtsy or bow when meeting a member of the Royal Family as it shows “respect and good manners”, says Mr Partridge.

“Nowadays, it’s a nod to tradition. The Queen is quite relaxed about it however and a simple handshake will suffice.

“She wants people to feel comfortable, so they should do what’s best for them. But I think people do like the idea of tradition.”

Image copyrightGetty ImagesImage caption Joan Collins goes for the curtsy when meeting the Queen at the Royal Academy in 2012

Ms Money-Coutts says the whole notion can seem faintly ludicrous now, adding: “Curtseying was from the days of big crinoline skirts and they would fall very dramatically – the deeper the curtsy, the more effective it was.”

But, she adds: “It’s mad, but I love it. It’s quite eccentric.”

What are the rules on who gets the curtsy treatment?

There are fairly complicated rules about which royals curtsy to whom, as Mr Partridge explains.

“For example, the Duchess of Cambridge and Duchess of Sussex curtsy to royal princesses by blood – unless they are with their husbands, in which case the princesses would curtsy to them instead.”

Well, that makes total sense.

Image copyrightShutterstockImage caption Princess Diana curtsied as she met Queen Sofia of Spain in April 1987

Ms Money-Coutts adds: “I do wonder what happens behind closed doors and if they bother with all that bowing and bobbing when they’re coming down to breakfast.”

What are the faux-pas to avoid?

“It should be a dignified and discreet bob,” says Ms Broke-Smith. “You don’t want to be like one of those opera singers who wave their right arm around as they curtsy.

“It’s almost too dramatic and making a point.”

Mr Partridge adds: “You do find people can go overboard and do very flamboyant curtseys and bows. These big, grandiose gestures are a bit over the top.”